Embedded systems often employ some form of asynchronous serial communication with other devices. Usually a coprocessor will manage the intricate details of the serial protocol(s) used for communication. In the absence of a coprocessor, the task of servicing serial devices will fall on the main processor, thus consuming valuable resources and imposing burdensome priority and timing requirements. Most serial protocols typically have stringent timing requirements. Without a coprocessor, the main processor handling the serial communication task will need a detailed knowledge of the system hardware to exploit the processor's capabilities. Knowledge of the system hardware entails knowing about low-level device driver routines, which are often prone to errors. In that regard, the main processor must verify a serial device's compliance as well as ensuring its own compliance. Taking a generic approach with regard to processor priorities can waste processor resources. Setting task priorities too low can cause missed deadlines due to task pre-emption resulting from other tasks running at higher priorities Setting task priorities too high can block critical tasks and waste processor time.
Thus, there is need for a technique for achieving asynchronous serial communication in the absence of a co-processor, which overcomes the aforementioned disadvantages.